What is the Counting of the Omer?
The Torah teaches that the days between Passover and Shavuot are to be counted (Lev. 23:15-16; Deut. 16:15-16). These days of "counting" refer to the period within which the obligation to bring an omer of barley from the harvest as a "first fruits" offering to the Temple was to be fulfilled. The days of counting, which lasted a period of seven weeks, are called, in Hebrew, Sefirat Ha'Omer and are likened to a connecting thread between the Passover from Mitzrayim [biblical Egypt] and the giving of the Torah at Sinai. According to the Sefer HaChinuch [Book of Education, 13th Century, Spain1] the purpose of the redemption from Egypt was the giving and reception of the Torah at Sinai. Counting the Omer between Passover and Shavuot 50 days later signifies the commitment of Jews to the promise of Sinai.

Because Shavuot marks the end of the 49 days of [the counting of] the omer Shavuot is also referred to as the Feast or Festival of Weeks. Shavuot, being the 50th day after Passover, was named Pentecost by Hellenic Jews. [Pentecost is Greek for “Fiftieth.”]

The Spiritual Importance of Sefirat Ha'OmerA spiritual understanding of Counting of the Omer [Sefirat Ha'Omer] is connected to the physical exodus from Mitzrayim and the spiritual freedom received in the giving of the Torah at Sinai, which is celebrated at Shavuot. The physical bringing of barley sheaves during the 49 days period between Passover and Shavuot helps make a spiritual connection between the the two festival events

The redemption from slavery is not complete
without the reception of the Torah at Sinai.

Origins of Lag Ba'OmerLag Ba'Omer (falling on 18th Iyyar) is the 33rd day of counting the omer.

According to a tradition recorded in the Kitzur Shulchan Aruch(120:1-10), Lag Ba'Omer signals a small break in the counting of the omer to celebrate the ending of the "great plague", a perceived "divine sent" plague experienced during the Counting of the Omer in Rabbi Akiva’s time (2nd Century CE). The Talmud relates (Yevamoth 62b) that 24,000 of Rabbi Akiva's disciples died at the same time because "they did not treat each other with respect" and subsequently the "world" remained desolate of learning until R. Akiva taught new masters. These new masters [R. Meir, R. Judah, R. Jose, R. Simeon, and R. Eleazar b. Shammua] revived the Torah.

Another tradition suggests that R. Akiva's students died at the hands of the Romans during the Bar Kochba revolt. The celebration of Lag Ba'Omer with a break in fasting and the lighting of bonfires is, perhaps, a reflection of this tradition.

Yet another traditional celebration by some Jews at Lag Ba'Omer is the memorial of the death of R. Shimon, one of R. Akiva’s five students who survived the plague. It is a kabbalistic belief that through one of R. Akiva's five students who survived the plague, R. Shimon ben Yohai Israel received the mystical Torah, The Zohar. This hidden and mystical Torah transmitted through R. Shimon is a complement to the revealed Torah given through Moses. Lag Ba’Omer is remembered as the anniversary of R. Shimon ben Yohai [aka. Rashbi; R. Simeon,] who referred to the day of his (future) passing as “the day of my happiness,” instructing his disciples to observe the day as a day of joyful celebration.

The Meaning of “LAG”
The word “lag” is a shorthand way for writing 33, a number which is written in Hebrew as lamed gimel [לייג
]. Lag Ba'Omer is thus the 33rd day of the counting the omer. An omer (sheaf) is a biblical measure of barley. The counting of the days “in the omer” [ba'omer = “in the omer”; Shephardic Jews call the days “la'omer” meaning “of the omer”] is a practice which dates from biblical times (Lev. 23:15-16) when, from the second day of Passover through to Shavuot [seven weeks], a sheaf of barley the size of an omer was brought to the Temple in Jerusalem. Following Shavuot the offering changed from barley to wheat, signaling the start of the wheat harvest.

A Kabbalist’s approach to Lag B’Omer
A Kabbalist finds in Lag B’Omer a day to celebrate life and hope amidst days of mourning.

On theJewish calendar, Lag B’Omer is on 18th of the month of Iyyar. Eighteen is written yod, het [יח] in Hebrew. The kabbalists looked at yod het and rearranged the letters to het yod, which is Chai [חי], the Hebrew for Life. The Hebrew word Chai is [by Gematria2] numerically equivalent to 18. According to this spirituality, Lag B’Omer is a break in the days of the omer and the traditional practice of fast/restraint during this period to celebrate LIFE.

Thus Lag Ba'Omer gives life to the month of Iyyar, and by extension infuses our life with a healthy measure of joy, optimism, and hopefulness.

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[1] The Sefer HaChinuch is an anonymous work published in the 13th Century in Spain, which discusses the 613 mitzvot (commandments) of the Torah from legal and moral perspectives, drawing upon their biblical
sources and developing their philosophical meaning and their understanding as halakhah. The work has been attributed to R. Aharon HaLevi of Barcelona [Ra'ah] a colleague of Rashba [R. Shlomo Ben Aderet] but, because of contradictions between the Chinuch and his Ra'ah's works, many believe that Sefer Chinuch is the work of another Aharon HaLevi, a student of Rashba rather than his colleague.
[2] Gematria is a system wherein a numerical value is assigned to each letter of a word or phrase which then gives rise to a new or dual meaning or relationship between the words.